Change Validator checks based on project type

[redrun45]

This is a (perhaps mild) annoyance when cataloging, for three projects every two weeks. MCs need to ignore the failing checks, and do their equivalent checks manually.

Currently, Validator runs the same set of checks against each type of project. For weekly and fortnightly poetry, the following checks from Librivox_filecheck.php will always fail:

• file_length - the current minimum is 5 minutes. Other poetry projects are probably also short of this, but we might not want to shorten this limit globally. MCs can discuss that option, or we can special-case the weekly and fortnightly poems.
• chapter_name - the special-casing for poems here doesn't seem to work - I think they're in the DB as poetry_weekly and poetry_fortnightly instead of just poem.
• filename_chapter - I'm not really sure what this one does. Experimentation needed. 🤔
• tracknumber - this one expects the files to be named with track numbers matching their order, but the weekly and fortnightly poems use the readers' initials instead (see example message below). Files do still need to sort in alpha-numeric order, so perhaps we could have a different check for this.

An example message shown to the MC, as given under 'check_file_completeness'
Expecting file #1 to have name amongtherocks_browning_01_128kb.mp3 DEBUG:(1::0::amongtherocks_browning_aps_128kb.mp3)